Method of extractively separating mixed metallic species



Oct. 6, 1964 Filed Sept. 2, 1959 H. SMALL 3,151,931

METHOD oF EXTRACTIVELY SEPARATING MIXED METALLIC SPECIES 2 Sheets-Sheet 2 Fig 5 SEPHRHT/OA/ OFLa, Yb HND Tm US/NG DOWEX5O RES/N 9A/0 0](2-57/1'11. HEXVL) PHOSPHOR/C H670 (HE/P) F /M H05/ip r- IN VEN TOR.

l Ham/ISA 5ma// O 8 6 24 3 2 40 BY Fracf/'on Number M fia/ HTTORNEY Oct. 6, 1964 H. SMALL 3,151,931

METHOD OF' EXTRACTIVELY SEPARATING MIXED METALLIC SPECIES Filed Sept. 2, 1959 2 Sheets-Sheet 1 SEP/@RH TlO/V 0F THOR/UM QA/0 RHRE 14197' H5 50% raf? 60% 7.5,@ Feed oZXy/ene 202 Xy/ene 2. Z N0 Vo /ume f77/06H6, mfg JNVENTOR.

nog: 2 Hom fsf: `Srnov// Arron/VU United States Patent O 3,151,931 METHOD F EXTRACTIVELY'SEPARATING MlXED METALLIC ySPECIES Hamish Small, Midland, Mich., lassigner .to rThe Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed Sept. 2, 1959, Ser. No. 837,628 Claims. (Cl. Zit-14.5)

This invention concerns a method for the extractive separation of mixed heavy metal species. More particularly it concerns a method for extractively separating mixed heavy metal species by a procedure involving an aqueous extraction with a novel stationary aqueous phase, an ion exchange resin having the aqueous extracting medium absorbed in its granules, whereby the heavy metal species are selectively extracted from their solution in a Water-immiscible organic medium and eluting the absorbed metal values by contact with a water-immiscible liquid organic medium which is a selective solvent for the metal values.

This invention diiers from the known art of countercurrent liquid-liquid extraction in that `the aqueous phase is replaced by a stationary column of ion exchange resin particles swollen with absorbed water. -In this way, one benefits from the low theoretical plate height (many theoretical stages) of a column chromatographic technique. In addition, the process of this invention does not suffer from emulsication problems and accompanying entrainment losses encountered in conventional liquid-liquid extraction processes. This invention is particularlyrapplicable to the separation of rare earths and thorium from rare earths.

In one aspect of this invention, a column ofA an anion exchange resin in the salt form, the particles of which are water swollen to any desired extent upto the maximum (maximum swelling resulting when the resin is contacted with Water until it no longer swells, asdetermined by a simple test) is contacted with a solution, of, heavy metal salts of an inorganic acid in a solvent which contains a water-immiscible organic liquid in which ,the Vsalts are soluble as ion association complexes, containing, if desired, a small amount of an inert organic water-immiscible diluent. The heavy metal salts are thereby selectively distributed between the organic and aqueousaphrases. Thereafter, the metal salts absorbed in the'water held by the anion exchange resin particles are selectively eluted with a water-immiscible organicgliquid in .which ,theyware soluble.

Any amine type organic anion exchange resins, e.g., those disclosed in U.S. LPatents 2,591,573,7and 2,591,574 and equivalents thereof, are operable in this process. As solvents for the heavy metal salts of inorganicacids are used those water-immiscible liquid organic media as are known to dissolve the particular species by ion .association, e.g., the trialkyl phosphates.havingfroml- :to carbon atoms per alkyl group of the straight or branched chain types, such as tIi-n-butyl, tri(2ethylhexyl), tride'cyl, tri-tetradecyl, tri-octadecyl, tri-eicosyl, and similar types. Typical solvents are indicated byl Morrison andFreiser, Solvent Extraction in Analytical Chemistry, 1957, pp.,4 6, and in sections of Part 3 of theirk book, pp. 12S-,156. The water-immiscible organic'solventsvare :those ,which will not mix with water but whichwill dissolve orextract heavy metal salts of inorganic acidsdissolved inwater by forming ion association complexes. Thel water-immiscible solvents are used as such or in admixture withva water-immiscible diluent, eg., anaromatic hydrocarbon. kerosene, etc.

A simple trial suflices to determine the rate of feed of the liquid organic water-immiscible lsolution of metal salts to the water-swollen anion exchange-resin column,

ICC

sincethe rate of feed varies with the type of metal .species vrto be yseparated as well as with the concentrationof the organic phase. The amountof absorbed water desirable .in the `water-swollen anion exchange resin column will ,becausetheinventionis widely applicable to so many .dif- 4.ferent heavy metal species. i

,In another aspect yoflthis invention, a column of a `cation exchangeresinin the ,acid form, the particles of which are swollen with absorbed water, is contacted with a solution of1heavy metalsalts in an acidic ester ofphosphoric acid, i.e., a monoalkyl or dialkyl ester of lphosphoric acid, if desired also containing a water-immiscible inert organic liquid diluent, e.g., van aliphatic or aromatic hydrocarbon or mixture thereof, such as kerosene or toluene or equivalents. The heavy metal species as salts of acidic alkyl phosphates, selectively exchange onto the cation exchangeresin column.' The metallic speciesare thereafter selectively eluted, nsing the same ora different acidic ester of phosphoric 4acid as was used in preparing the organic solutionof mixedmetal salts of -the'acidic phosphate ester. Operable cation exchange resins are the well known sulfonic acid and carboxylic acid types, of which the former are preferred. Representative cation exchange resins ,useful'lin the practice of the invention are disclosed in'UfS. Patent 2,366,007.

Metal salts are those of theA acidic monoalkyl yand dialkyl esters of phosphoric acid, the alkyl groups of which contain from"4 to 20 carbon atoms of the ,straightl or branched chain typesf i ,Instead of using anrorganic water-immiscible solution `of metal salts of anacidic phosphoric acid ester, a solution of heavy metal salts ofan inorganic acid in such an organic solvent forvsuch salts as was disclosed in` theiirst aspect of v'this invention'can ybe used. When contacted with water-swollen particulate cation exchangekrsins, the heavy metal species Vare selectively extractedV by the water in rthe resin and exchanged onto the fion exchange column. Thereaftergthe metalspecies are elutedselectively using anV acidic alkyl phosphoric acid ester'tas such AorV admixed with an inert water-immiscible organic diluentlsuchfas kerosene or toluene. Alternatively, acidic solutionsof a mineral acid and a water-immiscibleorganic solvent such as kwasrdiselosed in the iirstvaspect of this invention can be used fof elution. 'Y

In the iirst aspect ofl this invention, the anion exchange resin is advantageously surface etherified or treated with a small percentage yof, anionic wetting agent to inhibitagglomeration of the resinrparticles in the organic solvents. Etheriiication is Vcarried ',outby refluxing the cross-linked vinylaromatic resin` containing halomethyl groups on the aromatic nuclei, used in making the anion exchange resins, with a solution in ethanol of about 4 percent sodium Yhydroxide sufficient vto cover the resin beads. Because of inherently poor penetration of theAalcoholYinto the resin beads containing haloniethyl groups, the etherication reaction is restricted toasurface skin. Reilux time of about 3 Ahours sutices, afterwhich the surface etheried Ybeadsare washed free Yof .sodiumk hydroxide and Spdium ,Chloridewith ethanol- The resin .beads are thereafter converted Vto polyamine or :quaternary ammonium anion exchange resinrinl thenusualrrnanner. the second aspect of ,this invention, ,wherein an organic solutionof heavy metal salts of monoalkyl or dialkyl phosphoric acid esters is contacted with acolumn of `water-swollen cation exchange resin, it is preferable ythat the resin not be completely Water-swollen, otherwise a barrier layer of water forms on the surface of the beads and interferes with exchange of metallic species between the organic solution and the cation exchange resin. In general, the water content should not exceed about 80 percent of the completely water-swollen resin in order to permit good absorption. This is accomplished by air drying the water-swollen cation exchange resin to an appropriate water content not exceeding 80 percent of the completely water-swollen state or by rehydrating air dried cation exchange resin by suspending it in a hydrocarbon, e.g., toluene, containing a small amount of an emulsifying agent and gradually adding water While agitating the mixture. The water becomes emulsitied and is absorbed by the resin. Addition of water is stopped at the desired level. In all aspects of this invention, the interstitial volume of the resin bed is occupied by a water-immiscible liquid organic medium which is miscible with the organic solution of the heavy metal speces to be separated.

The following examples are in illustration of the invention and are not limitative thereof.

EXAMPLE 1 T horum-Rare Earth Separation (l) Preparation of resin and resin column. A surface etheried quaternary ammonium anion exchange resin, as described above, was used. The surface treated resin was loaded into a 1/2 LD. burette type column with xylene occupying the interstitial volume of the resin bed.

Resin: Dowex 1X4 (NO3) quaternary ammonium resin, 20-50 mesh, surface ethered, 48 percent water, volume of bed 90 mls.

(2) Preparation of feed solution. The feed solution was prepared as follows: solutions of thorium nitrate and rare earth (RE) nitrates (Lindsay Didymium Nitrate7 Code No. 450) in 50/50 volume: tri-n-butyl phosphate (T.B.P.)/xylene were prepared by shaking a volume of the mixed solvents with the respective solid nitrates. Equal volumes of the resulting nitrate solutions were mixed to give the feed solution. The composition of the feed solution was: 0.28 M in Th (NO3)4; 0.21 M in RE (Noah.-

(3) One hundred mls. of the above feed solution was loaded onto the prepared column at a flow rate of approximately l mL/min.

(4) Elution. Two eluants were used to effect separation. After loading, the column was rst eluted with 80 mls. of a 50/50 mixture of T.B.P./xy1ene by volume. This was followed by an elution with an 80/20 mixture of T.B.P./xylene.

(5) Analysis. Fractions of the efuent product were collected and analyzed by X-ray fluorescence. The locations of the thorium and the two major rare earths in the effluent are illustrated in the accompanying FIGURE l, wherein CE/CF is concentration in effluent to concentration in feed. Three large cuts from the eliluent product, denoted cuts 1, 2 and 3 on FIGURE 1, were extracted with water. The metals in these extracts were precipitated as their oxalates which were then washed, dried, and ignited to the oxides. The composition of these cuts is given in the table below:

TABLE I.-SEPARATION OF THORIUM FROM RARE EARTHS It was possible by this procedure to obtain a cut which contained pure thorium nitrate.

EXAMPLE 2 Rare Earth Separation (l) Preparation of the resin and the resin column. A

.4 surface etheried Dowex 1 resin was used. A column of resin was prepared by placing the resin in a 1/2 in. I D. burette type column with kerosene occupying the interstitial volume.

Resin: Dowex l (NOS) resin 20-50 mesh, surface etherified 48 percent water; volume of bed=85 ml.

(2) Preparation of the feed. Feed was prepared by shaking an organic phase (8O percent V.V.T.B.P./ 20 percent V.V. kerosene) with the solid rare earth nitrates. The source of the nitrates was Lindsays Didymium Nitrate, Code No. 450. The rare earth nitrates dissolved in the organic phase to give a solution which was approximately 0.7 M in rare earth nitrates.

(3) Application of feed solution to column. Eighty-five ml. of the above solution was loaded onto the prepared column at a flow rate of approximately 1 nil/min.

(4) Elution. An elution was carried out using 80 percent T.B.P. in kerosene as eluant at a flow rate of ca. 1 mL/min.

(5) Analysis. Fractions of the effluent solution were collected and analyzed by X-ray fluorescence.

The elution waves of the individual rare earths are shown in the accompanying FIGURE 2. The levels of rare earth in the eluent are expressed as the ratio:

C /C concn. of rare earth in efliuent E F concn. of rare earth in feed solution tained:

TABLE IL-ANALYSIS OF OXIDES Percent Metal in Oxide Cut No.

Y Dy Sm Gd Nd Pr La 2 0. 8 l l0. 8 6. 6 53. 5 7 2 3 0.4 0. 1 5. 7 1. 2 57. 0 8 10. 6 4 0. 3 O. 05 2. 8 0. 1 52. 0 9 21. 0

EXAMPLE 3 (a) Preparation of resin-A quantity of Dowex 50X4 (H+ form) sulfonic acid cation exchange resin, 50-75 mesh, was air-dried and its Water content determined. This resin was added to about live times its volume of toluene containing about one percent of a non-ionic emulsifying agent, glyceryl trioleate. The suspension of resin in toluene was rapidly agitated and water added slowly to the mixture. The water became emulsied in the toluene and in turn was absorbed by the dried resin. Addition of water was stopped when the moisture content of the resin reached 50 percent. The amount of water to be added was calculated knowing the weight of air-dried resin and its initial water content. The resin was then loaded into a 1/2 LD. burette type column with toluene as the fluid occupying the interstitial volume of the bed. The Volume of the bed was 47 ml. and its depth 12 in.

(b) Preparation of feed soluton.-The feed solution was prepared as follows:

A quantity of 25.5 g. of rare earth carbonate (equivalent weight 76.2) was added to 1115 ml. of a 1 M solution of di(2-ethy1hexyl) phosphoric acid in toluene. The suspension was stirred and all but a small amount of the solids dissolved. The solution was ltered to remove insoluble matter. The composition of the feed solution was 1 M in di(2-ethylhexyl) phosphate, 0.67 N in exchangeable hydrogen and 0.31 N in rare earths.

(c) Loading-The above feed solution was loaded to the prepared bed at a ow rate of 0.5 to 0.6 nil/minute.-

salts are dissolved in a water-immiscible'liquid organic solvent of the group consisting of trialkyl `phosphates and acidic alkyl-phosphoric acidestershaving 1 to 2 alkyl groups, the alkyl Vgroups of each of which group members have from 4 to 20 carbon atoms, andthe ymetal salts are ythereafter selectiyely,extracted from said solution thereof yby `contact with an aqueous liquid inwhich the metal salts are soluble, the improvement wherein said organic solution of said-metalvsalts is contacted with a (e) Analysis-The eiiiuent was collected in fractions bed of water-swollen granular ion exchange resin having (each fraction ca. 7.80 m1.) and analyzed by `Xray water absorbed in the ion'exchange resin granules and fluorescence, eluting the absorbed metal valuesfrom the water-swollen The exchangeable hydrogen ion content of individual resin by contact with said liquid rorganic water-immiscible cuts was determined by titration with sodium hydroxide. solvent which selectively elutes the metal values.

The concentration of the total rare earths in the same 2. Method for separating at least two members of the cuts was obtained by difference. In the accompanying group consisting of lanthanide and actinide series metal FIGURE 3 two plots are presented: salts which comprises passing a solution of said metal (a) a plot showing the break-through of the total rare salts of mineral acids dissolved in a water-immiscible earths (RE+3) and liquid organic solvent of the group consisting of tri- (b) a plot showing the break-through of the individual alkyl phosphates the alkyl groups of which each have rare earths. from 4 to 20 carbon atoms, which forms ion association The level of an individual rare earth in the etliuent is complexes with said metal salts, into contact with a bed of plotted as the ratio particulate surface etheriiied anion exchange resin, the

particles of which are water-swollen by absorbed water CE/Cp=concentmtlqn m. the emuent whereby said metal salts are selectively extracted from concentrano m the feed said organic solvent by the absorbed water in the resin The felatlVe separations fol the fare earths S amply and thereafter selectively eluting said metal salts from demonstrated by the (b) plot. Six larger cuts of effluent said water-swollen resin with said water-immiscible liquid were made, denoted by cuts 1, 2, etc., on the (b) plot, Organic solvent. and these cuts were extracted with 3 M HC1 and the rare 30 3. Method of claim 1, wherein the water-swollen resin earths of the extract precipitated as their oxalates, washed, is a strongly basic quaternary ammonium anion exchange filtered and dried. The rare earth content of these six resin in the salt form. cuts was determined by X-ray iiuorescence. 4. Method of separating at least two members of the At the same time a sample of rare earth carbonate group consisting of lanthanide and actinide series metal feed material was also analyzed. The resin in the colsalts which comprises passing a solution, in an acidic umn after the loading cycle was removed from the colalkyl phosphoric acid ester having l to 2 alkyl groups umn, washed with acetone and eluted with 3 M HC1. wherein the alkyl groups have from 4 to 20 carbon atoms, The rare earths in the eluant were precipitated as oxaof said metal salts of said acidic alkylphosphoric acid lates WaShed, filtered, dried, and analyzed by X-ray uoresester, in contact with a water-swollen particulate cation cence. The analysis 0f the SiX prOduCt Cuts, the feed and 40 exchange resin, whereby said metal salt cations are sethe resin product are given in the table below. The lectively exchanged onto said cation exchange resin and analysis figures are normalized to yttrium as 100. thereafter selectively eluting said metal salt cations from Y Yb Tm Er Ho y Tb Gd Eu Nd Ce La EXAMPLE 4 Separation of the Rare Earths Lu, Yb and Tm (a) Preparation of reSI'm-The resin was prepared as in Example 3. Bed vol.=47.5 m1.

(b) Preparation of feed-An organic feed solution was prepared by extracting an acidiiied aqueous solution of the rare earth chlorides with 1 M di(2ethylhexyl) phosphoric acid.

The composition of the feed solution was: 1.01 M in di(2ethylhexyl) phosphate; 0.62 N in exchangeable hydrogen; 0.39 N in total rare earths.

The volume of this solution fed to the column was ml. Flow rate ca. 1 mL/minute.

(c) Elutz'0n.-Elution was effected with l M di(2ethyl hexyl) phosphoric acid in toluene at 1 mL/minute.

(d) Analysis.-Fractions of the eiiiuent product were collected and analyzed by X-ray uorescence. The elution waves of the individual rare earths (Lu, Yb, and Tm), shown in FIGURE 4, indicate the separations made.

What is claimed is:

l. In a method for separating at least two members of the group consisting of lanthanide and actinide series metal salts of diiferent kinds from one another wherein said said resin with at least one of said alkylphosphoric acid esters.

5. Method of claim 4, wherein the resin is a sulfonic acid cation exchange resin.

6. Method of claim 4, wherein the alkylphosphoric acid ester is di(2ethylhexyl) phosphoric acid.

7. Method of separating at least two members of the group consisting of lanthanide and actinide series metal salts which comprises passing a solution in a water-immiscible liquid organic solvent of the group consisting of trialkyl phosphates the alkyl groups of which each have from 4 t0 20 carbon atoms, which forms ion association complexes with said metal salts, of said metal salts, in contact with a bed of a water-swollen particulate cation exchange resin whereby said metal salt cations are exchanged onto said cation exchange resin and thereafter selectively eluting said heavy metal values from said resin with an acidic alkylphosphoric acid ester having l to 2 alkyl groups, which each have from 4 to 20 carbon atoms.

8. The method of claim 7, wherein the resin is a sulfonic acid cation exchange resin.

9. The method of claim 7, wherein the water-swollen resin is a completely water-swollen sulfonic acid cation References Cited in the tile of this patent @Xchange fesin- UNITED TATES PATENTS 10. Method of separating lanthanide series metal salts which comprises passing a solution, in an acidic alkylphos- 2728633 Arde? Dec' 27 1955 phoric acid ester having 1 to 2 alkyl groups wherein the 5 2840451 Katzm- June 24 1958 alkyl groups have from 4 to 20 carbon atoms, of mixed 2925431 Choppm Feb' 16 1960 lanthanide series metal salts of said acidic alkylphosphoric acid ester, in contact with a water-swollen, particulate OTHER REFERENCES cation exchange resin, whereby lanthanide series metal J- IIlOfg- & Nucl- Chem- V01- 4 (1957.), Slfafglll, P1?- salt cations are selectively exchanged onto said cation ex- 10 304-314 and PePPafd 326-343- COPY 1D SCICUIC L1- change resin and thereafter selectively eluting said metal blafysalt cations from said resin with at least one of said alkylphosphoric acid esters. 

1. IN A METHOD FOR SEPARATING AT LEAST TWO MEMBERS OF THE GROUP CONSISTING OF LANTHANIDE AND ACTINIDE SERIES METAL SALTS OF DIFFERENT KINDS FROM ONE ANOTHER WHEREIN SAID SALTS ARE DISSOLVED IN A WATER-IMMISCIBLE LIQUID ORGANIC SOLVENT OF THE GROUP CONSISTING OF TRIALKYL PHOSPHATES AND ACIDIC ALKYL-PHOSPHORIC ACID ESTERS HAVING 1 TO 2 ALKYL GROUPS, THE ALKYL GROUPS OF EACH OF WHICH GROUP MEMBERS HAVE FROM 4 TO 20 CARBON ATOMS, AND THE METAL SALTS ARE THEREAFTER SELECTIVELY EXTRACTED FROM SAID SOLUTION THEREOF BY CONTACT WITH AN AQUEOUS LIQUID IN WHICH THE METAL SALTS ARE SOLUBLE, THE IMPROVEMENT WHEREIN SAID ORGANIC SOLVENT OF SAID METAL SALTS IS CONTACTED WITH A BED OF WATER-SWOLLEN GRANULAR ION EXCHANGE RESIN HAVING WATER ABSORBED IN THE ION EXCHANGE RESIN GRANULES AND ELUTING THE ABSORBED METAL VALUES FROM THE EATER-SWOLLEN RESIN BY CONTACT WITH SAID LIQUID ORGANIC WATER-IMMISICIBLE SOLVENT WHICH SELECTIVELY ELUTES THE METAL VALUES. 